This invention relates to a catalytic support particularly appropriate for the manufacture of catalysts for the treatment of hydrocarbons, and comprises in particular at least one oxide of a metal from the SVI group of the Periodic Table of the Elements, in which is incorporated a small quantity of silica. The invention also comprises preferred methods for the preparation of such a support. Lastly, the invention comprises catalysts prepared from such a support, as well as the uses of these catalysts in reactions for the treatment of hydrocarbons, such as, for example, hydrodesulphurization, hydrodenitrogenation, hydrogenation, hydroisomerization reactions etc.
It is well known that the oil industry resorts to many procedures whose object is to selectively transform certain compounds that are present in the oil cuts in order to obtain products whose properties are suitable for the sought use. These procedures usually call for one or more solid catalysts which must be specifically adapted to the chemical transformation we wish to complete and to the requirements tied to the implementation of the procedure.
Many of these reactions are done in the presence of a somewhat significant quantity of hydrogen. This is the case, for example, in the hydrodesulphurization and hydrodenitrogenation reactions that are aimed at eliminating the undesirable compounds, sulphuretted and nitrogenated hydrocarbons respectively, from the oil cuts. It is also the case in reactions that take place in the isomerization procedure of paraffins, which applies essentially to high-gravity gasolines, whose octane number is higher.
In most of these procedures for the treatment of oil cuts, the catalysts traditionally used today consist essentially of a high porosity alumina support, on which is deposited an active phase that corresponds to the active sites of the catalyst. This active phase often consists of a function that favors the transfers of hydrogen (in particular a group VIII metal of the Periodic Table of the Elements), usually combined with another compound, specific to the sought activity, namely the reaction to be catalyzed.
However, in general, the activity of the traditional catalysts is now proving to be insufficient, taking into consideration the increasing requirements as far as performance of the industrial procedures are concerned. For example, nowadays it is essential to increase the efficiency of the hydrodesulphurization procedures in response to stricter and stricter environmental standards concerning the maximum content of sulphuretted compounds in fuels.
This is why many researches have been undertaken in order to develop new, more active catalysts that would make it possible to meet these objectives without having to significantly modify the existing units, which would then make it possible to avoid costly investments.
It is well known that the nature and properties of the support have a significant influence on the activity of a catalyst, and among other things the researchers have tired to replace the traditional alumina based supports with new supports, capable of conferring a greater activity on the catalysts. In particular, the oxides of the SVI group metals of the Periodic Table of the Elements, such as zirconia for example, quickly proved to be relatively interesting potential candidates.
As early as 1970, U.S. Pat. No. 3,686,095 mentions the theoretical possibility of replacing the alumina with zirconia or magnesia. However, this patent limits itself to describing a hydrodesulphurization catalyst consisting of an active phase (hydrogenating metal combined with a group VI metal) deposited on a support with a very high porosity consisting of an alumina mixed with silica, meaning a completely traditional type of alumina base catalyst. If it mentions, in a theoretical manner, the possible use of alternative oxides, it in no way describes how to effectively prepare supports consisting of such oxides that have enough porosity to serve as a base for the preparation of industrial catalysts.
Indeed, if the zirconia type oxides do have interesting properties, to date they have not proved to be very appropriate for the manufacture of supports of industrial catalysts, to the extent that obtaining an adequate porosity is the result of the loss of specific properties brought on by these oxides. Therefore, many attempts have been made to try and improve supports with bases of such oxides in order to turn them into catalytic supports that can be used in the industry.
Thus, U.S. Pat. No. 5,021,385 proposes a catalyst that consists of a support with a high porosity made of co-precipitated zirconia and titanium oxide, on which are deposited molybdenum oxide (2 to 30% by weight) and nickel or cobalt oxide (1 to 10% by weight) and possibly phosphorus.
The FR patent number 2,661,171 describes a synthesis procedure of a stabilized zirconia with a high specific surface, designed to serve as a support for a hydrotreating catalyst. The high porosity of this catalyst is obtained thanks to the impregnation, before the calcination, of the amorphous zirconia by a solution of a stabilizing element chosen from among yttrium, nickel, aluminum, titanium, and phosphorus.
U.S. Pat. No. 5,262,373 recommends the method called melted salt method for the preparation of a support with a zirconia, alumina, silica or titanium oxide base, alone or mixed; the preferred support contains zirconia, alone or mixed with alumina, and is designed, after depositing the nickel and the molybdenum, to serve as a hydrotreating catalyst.
FR patent number 2,709,432 claims a catalyst that contains a support with a specific surface that is greater than or equal to 150 m2/g, consisting of 60 to 99% by weight of zirconia and 1 to 40% by weight of oxide of at least one metal chosen from the group consisting of the metals of groups V, VI, VII, the noble metals such as ruthenium, osmium, rhodium, iridium, uranium, the phosphorous, arsenic and sulfur compounds. This support, essentially designed for hydrocarbon hydrotreating catalysts, is also prepared by the melted salts method.
In general, the catalysts proposed in the prior art as alternatives to the traditional catalysts on an alumina support have not proved to very satisfying because of their insufficient level of activity, meaning it is less than that of the traditional catalysts. Indeed, obtaining a high porosity of the support is done to the detriment of the additional activity brought by the metal oxide that is the alternative to the alumina. In other words, when we want to obtain a support that is sufficiently porous (which is indispensable to guarantee a good accessibility of the active sites to the molecules to be converted), we loose the specific catalytic properties that are the entire interest of theses metal oxides. This is why in general such catalysts are not currently used in industrial reactors.
In pursuing research in the field of catalysts with a zirconia base or other equivalent oxide base, the applicant has sought to act on the properties of these oxides. In doing so, it has been discovered that, surprisingly so, the zirconia or titanium oxide can become a material of choice that makes it possible to create excellent catalytic supports, provided its structure is of the crystalline type and is doped in an appropriate way with a small quantity of silica. Indeed it becomes possible to rigorously control all the characteristics of porosity without however losing the specific activity brought by these alternatives oxides. Thus the applicant has been able to develop industrial catalysts from a high porosity matrix, consisting essentially of metal oxides of the SVI group (of which zirconia and titanium oxide), where said catalysts have proved to have a level of activity that is greater when compared to the catalysts of the prior art.
Applicant has also discovered an original method of preparation that makes it possible to obtain such supports by controlling their porosity so as to obtain the desired active structures.
Thus, the applicant has developed a catalytic support that consists of a substantial quantity of at least one metal oxide of the SVI group from the Periodic Table of the Elements in which is incorporated silica, characterized by the fact that the mass ratio between the quantity of metal oxide of the SVI group and the quantity of silica it contains ranges between 5 and 70, that the metal oxide of the SVI group is in crystalline form and that the specific surface of the support is greater than or equal to 160 m2/g.
Here and in what follows, the characteristics of porosity (specific surface, pore volume and average pore radius) are given in reference to the method of determination called B.E.T (Brunauer, Emmett, Teller) well known in the art.
The characteristics of structure and texture of the support as set forth in the invention have been optimized by acting on its method of manufacture, in particular by incorporating a small quantity of silica in the metal oxide of the SVI group, based on a determined mass ratio, and implementing the appropriate heat treatments, so as to precisely control the crystallinity of the SVI group metal oxide. The applicant has thus been able to control the properties of these oxides, which allowed her to select the most active formulas, the object of this invention.
Compared to the prior art, the support as set forth in the invention makes it possible to create more active catalysts that are more appropriate for use in an industrial reactor. Indeed, it has a high porosity that guarantees the accessibility of the active sites to the reactants while preserving the specific additional activity brought by the replacement of the alumina by a metal oxide of the SVI group. In other words, the catalysts developed from such supports have sites that are both more active and more accessible, which contributes to their excellent performances.
In addition, the properties of the support as set forth in the invention are stable at high temperatures. In particular its high porosity does not deteriorate either in the operational conditions of an industrial reactor or when subjected to a strong heat treatment, contrary to a good number of prior catalysts whose support is not essentially alumina. This stability is an undeniable advantage of the support as set forth in the invention. In particular, the catalysts manufactured from this support will be perfectly regenerative under traditional conditions of regeneration (for example, in the case of hydrocarbon treatment catalysts, by oxidation arranged at an increasing temperature, so as to provoke the progressive combustion of the coke deposited on the surface of the catalyst).
Furthermore, compared to the traditional alumina base catalytic supports, the support as set forth in the invention makes it possible to prepare catalysts that have an increased activity under similar reaction conditions. In particular, the results of nitrogen adsorption and desorption kinetics tests on this support show that the pores of the latter have a specific shape, probably similar to a cylindrical cavity, which increases the speed of entry and exit of the reactants in the pores compared to supports with an alumina base that have pores whose shape can be assimilated to that of a bottle of ink, meaning with a restriction of the entrance/exit section of the pores, causing a risk of congestion of the latter. This phenomenon helps explain the activity gain observed for the catalysts made from the support as set forth in the invention.
Lastly, these catalysts can be fully used in reactors of the traditional type where all that is needed is to substitute them, totally or partially, for the catalysts on an alumina support. This makes it possible, in a simple and inexpensive way, to considerably increase the performances of the procedures being considered, in particular the hydrocarbon upgrading procedures.
At the same time, the applicant has developed a method of preparation that makes it possible to control the structure and the texture of the catalytic supports with a metal oxide base of the SVI group and thus prepare a support as described above.
Lastly, the applicant used this support to prepare a certain number of catalysts conceived essentially for the treatment of hydrocarbons.
Therefore, the invention also relates to the method for preparing the support, as well as any catalyst prepared from this support. These aspects will be explained in more detail in the description and examples that follow.
In this invention, the catalytic support plays an essential role, to the extent that the greater activity of the hydrotreating catalysts obtained in the end, meaning after the active phases have been deposited, depends mostly on the intrinsic properties of the support. These properties must therefore be very carefully controlled.
The catalytic support as set forth in the invention contains a substantial quantity of at least one oxide of at least one metal of the SVI group, where said oxide must imperatively be present in crystalline form, meaning it must not be in the amorphous state. Preferably, the SVI group metal oxide is in a crystalline form of the tetragonal type. The determination of the crystalline structure of said metal oxide is performed, in a manner well-known in itself, by X-ray diffraction.
In addition, the texture of the support is controlled thanks to the incorporation, in said metal oxide of the SVI group, of a small quantity of silica, with a given weight ratio: the content of SVI group metal oxide by weight of the mixture ranges between 5 and 70 times its content in silica, which corresponds to a silica content that ranges between 1.5 and 16% by weight in a mixture that would only contain these two oxides. Preferably the mass ratio between the metal of the SVI group and the silica ranges between 8 and 30. By silica, we mean any silicon oxide.
Preferably the SVI group metal oxide that is contained in the support is chosen from among zirconia, titanium oxide or a mixture of these two oxides. Preferably, said SVI group metal oxide is zirconia. By zirconia, we mean zirconium dioxide.
Preferably, the specific surface of said support is greater than or equal to 180 m2/g. Advantageously it has a pore volume that is greater than or equal to 0.25 cm3/g, preferably between 0.30 and 0.60 cm3/g included. Furthermore, its average pore radius is advantageously greater than or equal to 20 xc3x85, preferably ranging between 20 and 120 xc3x85 included.
Essentially, the catalytic support as set forth in the invention contains the mixture described above, consisting of metal oxide of the SVI group (in particular zirconia, titanium oxide of a mixture of both) in crystallized form, doped with silica.
In addition it can contain a variable quantity of another refractory metal oxide usually used in the industry and that, as known, the man of the art may consider good to incorporate for various purposes, for example in order to obtain or strengthen certain properties, in order to facilitate the preparation or the shaping of the catalyst, or yet to reduce the costs of manufacturing the catalyst by replacing part of the support with raw materials that are less costly or more available than the metal oxides of the SVI group.
In particular, the support as set forth in the invention can advantageously contain a binding agent that has been incorporated in order to facilitate its shaping. Such a binder can consist of any refractory mineral oxide usually used for this reason, and in particular can be chosen from the group consisting of aluminas, silicas, silica-aluminas, alumino-silicates, clays and mixtures of these compounds. Preferably, said binder consists of alumina. Advantageously it can be incorporated in a quantity that ranges between 0.1 and 30% by weight in relation to the total weight of the support.
The catalytic support as set forth in the invention is an appropriate base for the manufacturing of all sorts of catalysts called supported, that is containing one or more compounds, deposited on said support, and playing the role of active phase. Very diverse compounds can thus be deposited on this support based on the type of activity that is sought, or in other words, the reaction to be catalyzed.
When the catalyst is meant to be used in a procedure for the treatment of hydrocarbon cuts, said active phase advantageously contains at least one metal or one compound of a metal of VIII group of the Periodic Table of the Elements. The metals or metallic compounds of this family are indeed particularly known for helping the reactions that involve transfers of hydrogen (which is often the case in reactions that take place in hydrocarbon upgrading).
According to a first method of execution, the active phase consists of one or more metals or metal compounds of group VIII of the Periodic Table of the Elements. Said metal of group VIII can for example be nickel, with a content ranging between 15 and 30% by weight in relation to the total weight of the catalyst. It can also, as a non restrictive example, be chosen from among platinum and palladium, and can be present at a content ranging between 0.1 and 2% by weight in relation to the total weight of the catalyst.
The catalysts as set forth in this first method of execution are particularly appropriate for a use in hydrocarbon hydrogenation reactions.
On the other hand, a metal or metallic compound of group VIII can be combined with one or more additional compounds, metallic or not, chosen for their specific activity in the reaction to be catalyzed.
Thus, according to a second method of execution, said active phase consists of one or more metals or metal compounds of group VIII of the Periodic Table of the Elements combined with at least one compound of the acid type. The metals of group VIII are then preferably chosen from among platinum, palladium, ruthenium, rhodium, osmium, iridium, and nickel. Platinum, alone or combined with palladium, is particularly preferred. These metals are advantageously present at a total content ranging between 0.1 and 2% by weight in relation to the total weight of the catalyst. The compound of the acid type can for example contain sulfate ions or tungstate ions whose content is variable based on the degree of acidity being sought.
The catalysts described according to this second method of execution are particularly appropriate for use in reactions that require the use of an acid or superacid type catalyst, such as in particular paraffin or olefin isomerization reactions, naphtenic hydrocarbon decyclization reactions, alkylation reactions, oligomerization reactions, hydrocarbon dehydration reactions, and oil cut hydrogenation reactions.
These catalysts are also particularly advantageous for deep hydrodearomatization reactions and/or desulphurization of oil cuts, of which gas oils in particular.
Lastly, these catalysts have proved to perform particularly well in procedures for the treatment of hydrocarbonic cuts that contain a substantial quantity of long chain paraffins (more than 7 atoms of carbon), whether linear or slightly branched, such as for example paraffins from a synthesis of the Fischer-Tropsch type (hydrocarbon synthesis from the mixture CO+H2). The transformation of these paraffins by hydrocracking and/or hydroisomerization is often necessary in order to obtain either xe2x80x9clargexe2x80x9d products (gasolines, naphtha, middle distillates), or specialties (paraffins, sophisticated lubricants). The operational conditions must then be adjusted based on the reaction we wish to favor (hydrocracking or hydroisomerization), and the desired level of conversion. Advantageously, they can be the following: a temperature ranging between 20xc2x0 C. and 400xc2x0 C. (preferably between 150xc2x0 C. and 300xc2x0 C.), a pressure preferably ranging between 5.105 and 200.105 Pa, a hydrogen/hydrocarbon H2/HC molecular ratio between 1 and 20 (preferably between 5 and 15).
According to a third method of execution, which is the preferred method of execution of the invention, the active phase consists of at least one metal or one compound of a metal of group VIII of the Periodic Table of the Elements. Advantageously these two types of metals are deposited on the support in the form of metal oxides, which are then transformed, totally or partially, into corresponding sulfides (metal sulfides) during an activation step that precedes the use of the catalyst.
Preferably, said group VIII is cobalt and/or nickel. The catalyst as set forth in the invention preferably consists of 2 to 10% by weight of the corresponding metal oxide.
Preferably, said SVI group metal is molybdenum and/or tungstene. The catalyst as set forth in the invention preferably consists of 10 to 25% by weight of corresponding metal oxide.
The catalysts as set forth in this third method of execution are particularly appropriate for use in hydrotreating procedures such as, in particular, procedures of hydrodesulphurization, hydrodenitrogenation, hydrostripping or hydrogenation of oil cuts such as gasolines, gas oils, vacuum distillates, long residues or vacuum residues.
The implementation conditions for these hydrotreating procedures will be optimized according to the type of hydrotreating planned, but also according to the nature of the charge to be treated and the treatment rate we wish to reach. The operational conditions of the hydrotreating procedures are not substantially modified in the presence of a catalyst as set forth in the invention, when compared with the usual conditions in the presence of a traditional catalyst on an alumina support. These conditions are usually the following: a temperature ranging between 260 and 400xc2x0 C., a total pressure ranging between 20 and 200.105 Pa (between 20 and 200 bars), a hydrogen/hydrocarbon volume ratio ranging between 50 and 2000 normal-to-liter/liter, an hourly volume velocity of the charge preferably ranging between 0.2 and 10 hxe2x88x921.
Although the catalysts described above are the preferred methods of execution of the invention, in no way should they limit~its range. The man of the art can indeed create a large variety of supported catalysts from the catalytic support that is the object of the invention by depositing the appropriate active phases upon it.
The catalysts as set forth in the invention are of the solid type. They can come in all the forms to which the man of the art usually has recourse for the implementation of solid catalysts, and in particular in the form of particles such as beads, extrusions, pellets. They have an apparent filling density that usually ranges between 0.7 and 1.2 g/cm3.
The method used for the preparation of the support as set forth in the invention must make it possible to rigorously control its structural and textural properties in order to obtain a support that meets the characteristics of the invention and makes an appropriate base for the preparation of highly active catalysts that meet the requirements of the industrial procedures.
The applicant has developed a preferred procedure for the preparation of such a catalytic support. This procedure consists essentially of the following steps:
a) from a solution of at least one salt, at least one metal of the SVI group, precipitation of the corresponding metal oxide(s),
b) reflux ripening of the precipitate obtained,
c) addition of silica
d) ripening of the mixture, under agitation,
e) washing, filtration then drying of the solid obtained,
f) shaping of the solid,
g) calcination of the solid.
Advantageously the precipitation step (a) of the SVI group metal oxide(s) can be performed by adding a basic solution to a solution (for example aqueous) in which are dissolved the appropriate metallic salts. The basic solution used can be any solution that makes it possible, by increasing the pH, to carry out the precipitation of a hydrated oxide from a solution of a precursor salt of said oxide. For example, it could be an ammonia solution or any other base known to the man of the art.
Salts of the SVI group metals likely to be used in order to obtain a precipitate of an SVI group metal oxide are well known to the man of the art. When we want to obtain a support with a zirconia base, we use a zirconium salt that may for example be chosen from the group made of nitrate, chloride, acetate, formate, zirconium or zirconyl oxalate, as well as zirconium alcoholates. When we want to obtain a support with a titanium oxide base, we use a titanium salt, which for example can be chosen from among the titanium chlorides or the titanium alcoholates.
The ripening step (b) is performed by bringing the solution in which the SVI group metal oxide gel is precipitated to a reflux for a sufficient period of time, advantageously between 1 and 50 hours and preferably between 12 and 36 hours.
As far as step (c) is concerned, silica is added to the SVI group metal oxide gel. This addition can take place in various ways, for example by a direct addition of silica, or by adding a solution of a silicon salt followed by an in situ precipitation. In the first case, we add a solution containing a colloidal silica gel to the SVI group metal oxide gel. In the second case, we add a silicon salt solution (such as ethyl orthosilicate or sodium silicate) to the SVI group metal oxide gel and we cause the silica precipitation by adding an acid.
The ripening step (d) is performed by keeping the mixture of silica gels and SVI group metal oxide under a strong agitation for a duration that advantageously ranges between 1 and 100 hours. This ripening can be under reflux or at room temperature. Preferably, when the SVI group metal oxide is titanium oxide, it takes place under reflux.
Step (e) corresponds to a filtration of the resulting suspension in order to recuperate the oxide gel. The latter is then washed and dried at moderate temperature (preferably around 100xc2x0 C.), for example in an oven.
The solid shaping step (f) makes it possible to agglomerate the solid into a powder so as to form particles (for example beads, extrusions or pellets) in order to obtain a support that is qualified for the preparation of catalysts that can be used directly in an industrial reactor. In order to make this operation easier, it may be necessary to add a binder (alumina xerogels or any other industrial binder) to the power, then to mix this mixture before proceeding with the actual shaping by extrusion, xe2x80x9coil dropxe2x80x9d method or any other method known for the shaping industrial catalysts.
The support thus obtained undergoes a calcination step (g) that must take place at a temperature that is sufficiently high, advantageously ranging between 550 and 850xc2x0 C., for a duration that preferably ranges between 2 and 6 hours. This step is essential since it leads to the crystallization of the SVI group metal oxide. This calcination can advantageously take place under a controlled air flow.
The preparation of catalysts from the support as set forth in the invention is done in the traditional manner, by depositing at least one active phase on said support, according to methods that are well known to the man of the art. Of course, the method used will depend largely on the nature of the active phases to be deposited on the support.
For the deposit of metallic compounds, we can advantageously proceed by impregnation of the support using solutions of the metal compounds to be deposited, followed by a drying phase. For example, if we wish to deposit platinum on the support, we can proceed by impregnation using a solution of a platinum compound that can be chosen from the group consisting of chloroplatinic acid and complex platinum compounds.
When the active phase of the catalyst to be prepared consists of various compounds, they can, depending on their nature, be deposited either successively or simultaneously.
In particular, for the preparation of a catalyst that contains at least one metal (or metal compound) of group VIII combined with at least one metal (or metal compound) of the SVI group, it is preferable to deposit these various compounds simultaneously, through impregnation with a solution of a mixture of corresponding salts, followed by a drying phase.
Usually, such a deposit of an active phase is followed by a calcination step of the catalyst.
Furthermore, for some types of active phases it can be advantageous to proceed with the deposit before the completion of the preparation of the support and in particular before the calcination step g) of the support. This is the case for example for the active phases that consist of sulfides, tungstates or other similar compounds, whose grafting to the surface of the support is best when it is done before the first calcination (step g). For such active phases, it is therefore preferable to insert, in the sequence of preparation of the support, at least one step for the deposit of this active phase. Advantageously, said deposit step is inserted between steps e) and f), or between steps f) and g).
Lastly, before being able to use the catalyst in an industrial reactor, it is usually necessary to submit it to a final activation step (often completed in situ), for which the conditions, well known to the man of the art, depend essentially on the type of procedure being considered.
For example, in the hydrodesulphurization, hydrodenitrogenation and hydrostripping procedures, after having charged the catalyst in the reactor, we proceed with a previous activation step in situ, that consists in presulfurizing the active sites of the catalyst using known methods: in general, after putting the hydrogen under pressure between 50 and 200xc2x0 C., we increase the temperature to approximately 300 to 400xc2x0 C., making compounds likely to generate sulfur pass over the catalyst, such as hydrogen and hydrogen sulfide mixtures, thiols, disulfides or carbon sulfides or even a gas oil that contains sulfur.
The preparation methods described above are only suggestions for the execution of catalytic supports and catalysts according to the invention. Of course, they are not to be considered as limitations. Furthermore, the man of the art will be able, if necessary, to adapt the methods described through additional other well known operations, such as for example steps of solvent washing, drying, calcinations, and the incorporation of other usual refractory oxides.